Fingered electrodes for microfluidic single particle analysis

Abstract

The electrical properties of particle solutions can be investigated on a single particle basis by using micro fluidic channels. The impedance can be measured across the channel using at least one pair of conductive electrodes, at least one electrode of a pair being a fingered electrode having a plurality of fingers. The pattern of fingered electrodes creates a longer and more complicated measurement signal shape which leads to a significant improvement of measurement sensitivity. An application for the proposed technology is to significantly improve the measurement sensitivity of impedance measurements on blood cells, leading to a better differentiation between different types of white blood cells. Better measurement sensitivity also enables the measurement of smaller particles and higher throughput.

The invention claimed is: 
     
       1. A measurement device for investigating particles which are suspended in a carrier liquid, comprising at least a first pair of measurement electrodes for carrying out an electrical measurement of the particles, wherein at least one electrode of the pair of measurement electrodes is a fingered electrode having a plurality of fingers, wherein the fingers are positioned perpendicular to a flow of the carrier liquid and wherein the fingers are irregularly spaced according to a random sequence code, wherein the irregular spacing provides an improved signal to noise ratio for the measurement device. 
     
     
       2. The measurement device according to  claim 1 , wherein both electrodes of an electrode pair are fingered electrodes. 
     
     
       3. The measurement device according to  claim 1 , wherein a pattern of the fingers corresponds to a pseudorandom number sequence. 
     
     
       4. The measurement device according to  claim 1 , furthermore comprising a second pair of measurement electrodes. 
     
     
       5. The measurement device according to  claim 4 , wherein the second pair of measurement electrodes has at least one fingered electrode, wherein the fingers of one electrode of the first pair of electrodes are interdigitated with the fingers of one electrode of the second pair of electrodes. 
     
     
       6. The measurement device according to  claim 1 , wherein at least one of the fingered electrodes has a plurality of fingers with a non periodic design. 
     
     
       7. The measurement device according to  claim 1 , wherein at least one fingered electrode structure has a variable electrode finger width and/or variable spacing width. 
     
     
       8. A microfluidic system comprising a measurement device according to  claim 1 . 
     
     
       9. A cell sorter comprising a microfluidic system according to  claim 8 . 
     
     
       10. A method for investigating particles suspended in a carrier liquid, the method comprising
 carrying out an electrical measurement process on at least one particle using at least one measurement electrode pair of which at least one electrode is a fingered electrode having a plurality of fingers that are positioned perpendicular to a flow of the carrier liquid and wherein the fingers are irregularly spaced according to a random sequence code, wherein the irregular spacing provides an improved signal to noise ratio for performing the electrical measurement process, thus generating a measurement signal, and 
 determining from the measurement signal presence of a particle in the carrier liquid. 
 
     
     
       11. The method according to  claim 10 , wherein carrying out an electrical measurement process comprises impedance measuring. 
     
     
       12. The method according to  claim 11 , wherein carrying out an electrical measurement process comprises impedance spectroscopy. 
     
     
       13. The method according to  claim 10 , further comprising carrying out a reference measurement, and comparing a result of the reference measurement with the measurement signal. 
     
     
       14. The method according to  claim 10 , wherein determining from the measurement signal presence of a particle in the carrier liquid comprises correlating a model curve describing passage of a particle between the fingers of the at least one measurement electrode pair of which at least one electrode is a fingered electrode with a section of the measurement signal.